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main.go
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main.go
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package main
import (
"encoding/json"
"flag"
"fmt"
"log"
"os"
"path/filepath"
"runtime"
"strings"
"syscall"
"github.com/containerd/containerd/platforms"
"github.com/moby/buildkit/util/archutil"
ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
)
var (
mount string
toInstall string
toUninstall string
flVersion bool
)
func init() {
flag.StringVar(&mount, "mount", "/proc/sys/fs/binfmt_misc", "binfmt_misc mount point")
flag.StringVar(&toInstall, "install", "", "architectures to install")
flag.StringVar(&toUninstall, "uninstall", "", "architectures to uninstall")
flag.BoolVar(&flVersion, "version", false, "display version")
}
func uninstall(arch string) error {
fis, err := os.ReadDir(mount)
if err != nil {
return err
}
for _, fi := range fis {
if fi.Name() == arch || strings.HasSuffix(fi.Name(), "-"+arch) {
return os.WriteFile(filepath.Join(mount, fi.Name()), []byte("-1"), 0600)
}
}
return errors.Errorf("not found")
}
func getBinaryNames(cfg config) (string, string, error) {
binaryPath := "/usr/bin"
if v := os.Getenv("QEMU_BINARY_PATH"); v != "" {
binaryPath = v
}
binaryBasename := cfg.binary
if binaryPrefix := os.Getenv("QEMU_BINARY_PREFIX"); binaryPrefix != "" {
if strings.ContainsRune(binaryPrefix, os.PathSeparator) {
return "", "", errors.New("binary prefix must not contain path separator (Hint: set $QEMU_BINARY_PATH to specify the directory)")
}
binaryBasename = binaryPrefix + binaryBasename
}
binaryFullpath := filepath.Join(binaryPath, binaryBasename)
return binaryBasename, binaryFullpath, nil
}
func install(arch string) error {
cfg, ok := configs[arch]
if !ok {
return errors.Errorf("unsupported architecture: %v", arch)
}
register := filepath.Join(mount, "register")
file, err := os.OpenFile(register, os.O_WRONLY, 0)
if err != nil {
e, ok := err.(*os.PathError)
if ok && e.Err == syscall.ENOENT {
return errors.Errorf("ENOENT opening %s is it mounted?", register)
}
if ok && e.Err == syscall.EPERM {
return errors.Errorf("EPERM opening %s check permissions?", register)
}
return errors.Errorf("Cannot open %s: %s", register, err)
}
defer file.Close()
flags := "CF"
if v := os.Getenv("QEMU_PRESERVE_ARGV0"); v != "" {
flags += "P"
}
binaryBasename, binaryFullpath, err := getBinaryNames(cfg)
if err != nil {
return err
}
line := fmt.Sprintf(":%s:M:0:%s:%s:%s:%s", binaryBasename, cfg.magic, cfg.mask, binaryFullpath, flags)
// short writes should not occur on sysfs, cannot usefully recover
_, err = file.Write([]byte(line))
if err != nil {
e, ok := err.(*os.PathError)
if ok && e.Err == syscall.EEXIST {
return errors.Errorf("%s already registered", binaryBasename)
}
return errors.Errorf("cannot register %q to %s: %s", binaryFullpath, register, err)
}
return nil
}
func printStatus() error {
fis, err := os.ReadDir(mount)
if err != nil {
return err
}
var emulators []string
for _, f := range fis {
if f.Name() == "register" || f.Name() == "status" {
continue
}
dt, err := os.ReadFile(filepath.Join(mount, f.Name()))
if err != nil {
return err
}
if strings.HasPrefix(string(dt), "enabled") {
emulators = append(emulators, f.Name())
}
}
out := struct {
Supported []string `json:"supported"`
Emulators []string `json:"emulators"`
}{
Supported: formatPlatforms(archutil.SupportedPlatforms(true)),
Emulators: emulators,
}
dt, err := json.MarshalIndent(out, "", " ")
if err != nil {
return err
}
fmt.Printf("%s\n", dt)
return nil
}
func formatPlatforms(p []ocispecs.Platform) []string {
str := make([]string, 0, len(p))
for _, pp := range p {
str = append(str, platforms.Format(platforms.Normalize(pp)))
}
return str
}
func parseArch(in string) (out []string) {
if in == "" {
return
}
for _, v := range strings.Split(in, ",") {
p, err := platforms.Parse(v)
if err != nil {
out = append(out, v)
} else {
out = append(out, p.Architecture)
}
}
return
}
func parseUninstall(in string) (out []string) {
if in == "" {
return
}
for _, v := range strings.Split(in, ",") {
if p, err := platforms.Parse(v); err == nil {
if c, ok := configs[p.Architecture]; ok {
v = strings.TrimPrefix(c.binary, "qemu-")
}
}
fis, err := filepath.Glob(filepath.Join(mount, v))
if err != nil || len(fis) == 0 {
out = append(out, v)
}
for _, fi := range fis {
out = append(out, filepath.Base(fi))
}
}
return
}
func main() {
log.SetFlags(0) // no timestamps in logs
flag.Parse()
if err := run(); err != nil {
log.Printf("error: %+v", err)
}
}
func run() error {
if flVersion {
log.Printf("binfmt/%s qemu/%s go/%s", revision, qemuVersion, runtime.Version()[2:])
return nil
}
if _, err := os.Stat(filepath.Join(mount, "status")); err != nil {
if err := syscall.Mount("binfmt_misc", mount, "binfmt_misc", 0, ""); err != nil {
return errors.Wrapf(err, "cannot mount binfmt_misc filesystem at %s", mount)
}
defer syscall.Unmount(mount, 0)
}
for _, name := range parseUninstall(toUninstall) {
err := uninstall(name)
if err == nil {
log.Printf("uninstalling: %s OK", name)
} else {
log.Printf("uninstalling: %s %v", name, err)
}
}
var installArchs []string
if toInstall == "all" {
installArchs = allArch()
} else {
installArchs = parseArch(toInstall)
}
for _, name := range installArchs {
err := install(name)
if err == nil {
log.Printf("installing: %s OK", name)
} else {
log.Printf("installing: %s %v", name, err)
}
}
return printStatus()
}